Hey, just realized this might have been better to post to "Players Corner".  Not a big deal but if the admins want please feel free to move it there if for nothing else, house keeping.   

Thanks -

Jim

Hi guys,

I just played at a party last night with some guys that I've been jamming with - we're starting to put together a pretty good band.  This was our 6th or so session playing together and the singer has only been playing with us for the last 3 practices so this "gig" (party) was only his 4th time with us.  We played about an hour (we only felt comfortable playing about 12 songs of 25 we've been working on) and I think it went really well - the people kept saying how good we sounded, esp the singer - he is killer.  Well, I'm not happy with my sound.  I have a 1993 Marshall Valvestate 8080 Combo (80w) with the original 8 ohm Eminence OEM speaker in it.  The other guitarist is playing through a Peavy Valveking 100/120 W half stack.  Obviously, his sound is much fuller/deeper, with way more punch.  My amp sounds thin - I think it sounds like a toy.  He says it's the speaker and I need to get a 4 x 12 or at least a 2 x 12 sealed back.  I think that's part of it but I'm also suspecting the SS power amp in my Marshall just won't cut it.  In the room we practice in I can get a reasonable sound out of it but we were playing outdoors last night (backyard party) and my amp was just not putting out even though it's a 80w amp (well that's what it's rated for). 

Obviously, the simple solution would be to buy a half stack like his and that would be it - well, money's tight and I don't have the $700.00 or more it would take to do that (I want a good amp, not something cheap).  So some ideas I've got on how to "fix" my set up for minimal investment of cash. 

1) I have a separate speaker cab - a Jet City 1 x 12 that I got for super cheap at a local music store.  They were getting rid of all their Jet City stuff and the price was so low I couldn't resist.  It has a 16 ohm Jet City Speaker in it made by Eminence (not sure of the "model" as it just says Jet City on it) and is a totally sealed back cab.  So my question is: can I run this safely with my Marshall amp?  My amp has a hard wired cable going to the speaker and no "speaker output" jack.  I could install a jack really easily but it would just be coming off the same leads just going to a jack.  I guess my question on this is can I run the 16 ohm Jet City speaker cab without hurting my amp?  Also, related to that question:  can I parallel the Jet City cab with my amp speaker safely - this would be about 12 ohm load (parallel)?

2) As I mentioned about paralleling the Jet City cab and the internal speaker, if it's not safe can I install an 8 ohm power resistor (50w or more) wired in series with my internal speaker (or the cable) to raise the impedance to 16 ohms and with that in parallel with the jet city it would be ~8 ohm load for the amp.

NOTE:  One thing I've heard is that it's safer to go up in speaker impedance (like to 16 or even 12) than to go down (to 4 or 2) with a SS power amp (or any amp really) - is this true?  Does this matter?

3)  Is it ok to "seal" up my combo cab as it is now an open back (almost the entire rear is open)?   The other guitar player said it would make my amp overheat but there's nothing at the bottom of the chassis that is dissipating heat - no vents, no heat sink fins, just a bank chassis.  If needed I could put a small fan somewhere to help reduce the heat but at this time, the amp has no heat issues and is always pretty cool running so I'm not sure if this necessary.  Related to this, if I can seal it up, I'm thinking of leaving a "port" to see if I can "tune" it for best sound/bass response or should I just seal it completely.

4) Another thing is I've considered replacing the internal speaker with a high efficiency model like the Emi Wizard or even a Vintage 30 as I'm not sure of the OEM speaker's efficiency rating - probably sucks.  I've also heard good things about the Private Jack.  So that might be a low cost option - probably not more than $100.- dollars or so.  I've also considered replacing the speaker in the Jet City cab with a Wizard or Private Jack or something along those lines.  I'm open to any opinions on speakers that might be good for this (keep in mind that this amp is Marshall's attempt to create a JCM like sound in a lower priced SS/Tube hybrid amp so that's the sound "signature" that this amp is intended for).  Obviously, I'd do the internal one first but I was concerned that if I replaced it with an 8 ohm one, I'd have the same issues like I discussed in #1 (12 ohm total parallel impedance load).  If I replaced it with a 16 ohm, I'd have 8 ohm's in parallel but if I wanted to just run the internal speaker alone, I'd be back to a 16 ohm load.  So back to the question #1....is 16 ohm ok?

Well, sorry for the long email.  Really appreciate any insights from you guys on what would be the best option/solution or even if you have other ideas.  I realize that it would ever get to being the equal of the half stack but I'm just looking to get the sound NOT TO SUCK - as I'm feeling it does now.  I guess I really need more bass/low end, more punch/tightness, and I need to move more air. 

And yes, I fully realize that a longer term solution is to build a 50w or so Tube head and get a decent 2 x 12 or 4 x 12 setup.  I'm working toward that but I'm currently in the middle of a Tweed Deluxe build that is now in it's third year!  Still haven't drilled my chassis yet so I'm still not committed to my layout and keep changing it (the wonders of VISIO - I call it virtual amp building).  Anyway, after I get this issue resolved with my current setup and if I can get it to sound Ok (and I make progress on that Tweed Deluxe), I'll get to work on that 50 watter - probably a Trainwreck variant as I just love that tone it has. 

Thanks in advance for all the input/advice -

Jim  (aka Spud)

Prologue: 

BTW if you're interested here's my Tweed Deluxe stuff as it stands now:

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/AMPS/5E3/

Also, here's all my DIY and Guitar stuff on Photobucket:

http://s252.photobucket.com/albums/hh7/spudjds/Public/

I welcome any comments. 

Thanks again.

Hey all,

This link was posted over at AX84 -

http://homepages.which.net/~paul.hills/Heatsinks/HeatsinksBody.html

Interesting article. 

Jim

How about an old CPU heatsink from a dead computer?  Would that be usable given that you have some thermal goop to put on there.

Jim

Well, the guy asked that I not post it around on the internet and I said I would honor that request as I'm trying to keep in good graces so I can get his help if I run into issues.  I could maybe email it -

Jim

Thanks for all the great suggestions -

I did end up getting schematic from Orange so they are OK in my book.  Just that it's not very clear.  It was a gif of a scan of what appears to be multiple generations of Xeroxes.  Most stuff I can make out but some of the caps and resistor values are pretty un-clear so I'll have to guess. 

Another observation - from what I'm seeing the power amp chip may have been replaced.  The soldering job on it is different than the rest of the amp - which is very uniform and precise and shiny.  The chip looks sloppy and has a lot of flux residue.  Also the heat sink gunk is pretty messy - I'm thinking the chip has been changed out.  Heat issues?  Well, this lead me to looking at the heat sink - how the heat sink is oriented.  When out of the chassis it seems like the heat sink would be effective as the fins have air flow - looking down from the top they look like an E with the chip on the left, flat surface (here >E).  But with it IN the chassis, it gets rotated 90d so the flat surface (where the chip attaches) is now at the top and the fins are all pointing down now.  I'm thinking it could have overheated - probably was run a full volume for a period of time.  Could the chip be damaged? 

I'm think, new chip and either mod heatsink or get another one or even add a fan - maybe 120v?

Before I do anything, I'm going to get it back together and power it up and take some readings to see if I'm getting proper power and go from there.

Thanks -

Jim

Oh, I see - well I'll have to remove all the pots as they are soldered directly to the PCB across the front.  There are about 7 of them.  And the switches, about 3 or 4.

Thanks - I'll try to get the pics this weekend as I'll have some free time.

Later,

Jim

Thanks for the ideas - I'll try to get some pics of it but I've already removed the PCB. It has molex type connectors for each of external items: speaker, power supply, reverb send/rec, etc and all are labeled clearly.  Also, they are the idiot proof kind in that they are keyed - oh, and each is unique - 2 pins, 3 pins, 4 pins, etc - so it's no problem to put it back together - in fact I've done it once already. 

I should say that the idea of washing it with water is counter intuitive to me - in my mind water and electronics don't go together but you're much more experienced that I am so I'll have to go by what you say on that.  I'll see how vigorous I want to get.  I might try some alcohol (since it exporates rather quickly) to clean the tracks side but I'm afraid of getting anything liquid on the components - esp the ICs.  Just my ignorance/in-experience. 

Regardless, first thing is to get the pics up here and I'll get some measurements.  I'll put the board back in and start from there. 

Thanks again for all the help - oh, I know what you mean but I didn't bother with critiquing the seller as it's only cost me $24.- so far and the cab and speaker alone are worth more than that - at least from my point of view.

Jim

Picked up a broken Orange Crush 15R off ebay for cheap.  I asked Orange about schematics and got no reply.  Also on their un-official amp site the guys said that the SS ones made in China are like red-haired step children, they don't really support them - I guess they are viewed as throw away as they are so cheap.  Anyway, haven't been able find any schematic from any source - anyone have any ideas? 

From looking at the guts, it's a TDA030 chip power amp with 3 TL072 chip pre-amp, looks like a some kind of Sym Diode clipping circuit and reverb - so I guess the TL072 are for 3 pre-amp circuits, clean, dist and reverb send/recieve - does that sound reasonable.  It does make a very faint scratchy sound but that's it.  Also, from the look of the board something may have been spilled on/in it.  The outside shows no evidence of that but it was probably cleaned up to sell it.  Owner said it used to work but hadn't been used it in a while and when he pulled it out of his closet, it was like this. 

I suspect it might be a TL072 but need to get some and replace them - I'll add sockets while I'm at it as everything is soldered to the board.  The board itself is pretty spacious and not crowded at all, it's all through hole components and not SMT - so it's human accessible.  The cab is pretty attractive - orange and pretty "beefy".  If I can get it up and running I might sell it but if not I'll gut it and use the cab for my own creation  :tu: 

Well, if anyone has any ideas, send em my way.  Maybe I should try to trace the board out and make my own schematic - might be a useful exercise to learn something...DOH!   

Later,

Jim

Well, this one didn't have a layout for perf - it did have PCB etch mask but I haven't done that kind of stuff yet.  Kind of leary of the chemicals -    There was only the schematic so I decided to make my own perf - I've done it before with other pedals so I'm pretty confident I did it right but yeah, you're right, this way I have a lot more possible issues - build errors plus possible layout errors.  Proven designs are always quicker/easier to get up and running - but this is how I learn, doing stuff like this on my own.  Just need the stretch of time (and patience) to go through an end to end debug - I think it's got to do with the pots cuz when I wiggle some of the pot leads, it sounds ok for sec or 2 then starts back buzzing, etc.  Probably something shorted out there.  Hopefully something simple -

Jim

Hey, I haven't gotten it to work either but I'm the type that gets frustrated easily so I've not much patience for debugging.  I will get it working though, just need some period of continuous free time to sit down quietly and go to it.  Just not easy to get that. 

Best of luck and keep posting your results - I like to get ideas from people on my builds.  I ended up here so I could try to build a decent sounding SS guitar amp and I'm hoping to pick up some tips and ideas from you all.   

Jim

Will,

I used that to build an attenuator, it's a Wall Volume Control for speakers.  I got the 25w mono model from my local RS.  I was advised over at ppwatt forum to use a  4.7uF non-polarized cap across the in and out terminals to preserve highs at lower lower volumes.  It seems to work ok except when you turn it way low it tends to lose highs so I might need to use a diff cap.  Here's some pics of what I did with it.  The schematics are for a different type of attenuator that I never built not for this super simple one. 

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/MISC%20Projects%20and%20Ideas/Attenuator/?action=view&current=100_0575_1.jpg

It's in a Radio Shack project box and I put and in 1/4" jacks for in and out and a chicken head knob - I also marked the front with a white magic marker with min/max and a tic for each click of the volume control - mine is stepped and not a continuous volume control/pot - at min it's off (no sound) and max is 0 resistance so wide open.  Hope this helps.

Jim

Hi,

I've built the Plexizer that Mojotron developed but I'm still DEBUGGING it.  It's on DIYSTOMPBOXES (search for Plexizer or Plexi or Mojotron Plexi).  I created my own layout with DIYLC (also at DIYSTOMPBOXES). 

Here is a link to the thread at DIYSTOMPBOXES: 

http://www.diystompboxes.com/smfforum/index.php?topic=50207.0

And here is my Layout - still debugging it as it squeals and buzzes with very low output.  Mojotron built it and posted clips with it in the above thread.  Here's my layout (not quite verified): 

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/PEDALS/Plexi-izer/

The first is closest to what I actually built - still need to finish debugging it and update the layout if needed.

I was planning to use this as the preamp in combination with a chip amp power amp (one of: LM1875? or TDA2005? or LM3886? or ) and stick it into a car sub-woofer box I got for next to nothing (like $5.00) at Parts-Express (closeout sale).  It takes a 8" speaker so I figured the Jensen Mod 8 or even a Weber 8" of some kind.  Run it from either a wall wart or build the PS into the cab - that part I'm still deciding.

The Sub-cab is one of the grey carpet covered wedge things with the speaker on the slanted front.  There is about a 2-2.5" panel on the font where I figured I'd put the controls and input.  On the back there is a speaker in jack on a round panel.  There's plenty of room on the inside as the speaker sits at an angle and most of the interior is empty.  Only issue is where to put a handle but it's no biggie really. 

Oh, there's also the JCM800 emulator that I have a schematic for somewhere and I did a layout but it was really close to the plexizer overall - I think it adds 1 extra JFET.  I can post it but need to find it first. 

Jim

Hey JM thanks - so I can go to Home Depot and get a 1/16" sheet and cut it to 4 x 6" and use that for the LM1875?  Wow - cool idea.  I like that. With about a thicker piece like 1/8" - would that mean a smaller size?  By what proportion?

WRT to the heatsinkusa product: so I can use a 1" sized one for the LM1875 or does it need to be 3"?   I may go with the 5.x size if it means I can get smaller piece - it's rated at 1.15 vs 2.3 for the 4.x" one I linked. 

So is there a formula to calculate this or some rule of thumb to go by?

Thanks for the info -

Jim

Hey - well I like it, here's my implementation of it - called the Small Fry to avoid confusion with the original:

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/AMPS/SF/

I added a tone control (By-passable) with a scooped switch.  Also added a switch to allow use of a ECC99 in addition to the 12au7 - rest of it is stock.  I recently re-did the grounds and I have a problem to debug with the boost - no work.  Oh, well - I can't leave well enough alone 

My mods are all documented in the layout and the schematic there. 

Jim